The investigation of smoking materials other than conventionally processed tobaccos has been the subject of increased interest in recent years. This interest has been generated primarily by the desire to alter the composition of smoke produced by smoking products based on conventionally processed tobaccos. It is possible, for example, to lower the quantity of nicotine in the smoke of a cigarette by replacing a portion of the tobacco with specially processed smoking materials containing little, if any, nicotine.
A large body of art exists which involves chemical and/or thermal degradation of carbohydrates in the preparation of smoking materials. The degradation products are combined with various inorganic salts, binders, flavorants, dyes, etc. and formed into sheets or shreds which are intended to simulate tobacco. These smoking materials have never duplicated the flavor and aroma of tobacco although they have met with a certain degree of success in providing a product with acceptable burn and ash characteristics. These tobacco substitutes have not found widespread consumer acceptance because they are composed largely, if not completely, of non-tobacco materials which produce flavor characteristics that are foreign to consumers of smoking products containing the substitutes.
A smoking product which seeks to retain the smoking characteristics of tobacco while at the same time realizing the advantages of thermally degraded carbohydrate materials is disclosed in U.S. Pat. No. 4,002,176. That patent describes the thermal degradation of tobacco in the presence of a catalyst at 100.degree. to 300.degree. C. until the weight of the thermally treated tobacco is preferably between 70 and 90 percent of the original weight. The catalysts employed are typically acidic in nature and it should be noted that column 2 of the patent teaches that tobacco heated in the absence of catalyst does not produce a satisfactory material.
Another method for the thermal degradation of tobacco is disclosed in U.S. Pat. No. 4,244,381. Tobacco by-product materials, particularly stems, are subjected to a heating step at 150.degree. to 370.degree. C. to give a weight loss of 10 to 35 percent and to a water extraction step to remove water-soluble constituents. The order in which these steps are carried out is not critical but the treatment conditions must be carefully controlled so that the treated tobacco materials can be incorporated directly into a smoking product without subsequently forming the treated materials into a sheet. The teachings (see Example 2) indicate that the water extraction step is essential.
Another smoking material which contains thermally degraded tobacco is disclosed in U.S. Pat. No. 4,256,123. Tobacco by-product materials such as stems, stalks and fines are subjected to pyrolysis at temperatures up to 700.degree. C. and the pyrolysis product is homogenized with untreated tobacco parts in a conventional reconstituted tobacco manufacturing process. The patent teaches that the proportion of pyrolyzed tobacco by-product which can be incorporated into such a reconstituted tobacco is preferably less than 0.6 part per part (dry weight) of untreated tobacco and is typically used in amounts of approximately 0.15 part of pyrolyzed material per part of untreated tobacco. Of particular interest in the patent disclosure are data showing comparative reduction of total particulate matter (TPM) and nicotine in cigarettes containing the disclosed reconstituted tobacco with pyrolyzed tobacco by-products as well as a similar reconstituted tobacco containing activated carbon instead of the pyrolyzed tobacco by-products. The cigarettes containing the pyrolyzed tobacco were found to give a greater reduction in both TPM and nicotine. Although the pyrolyzed tobacco by-products material is a desirable component in cigarettes and other smoking products, its impact on smoke composition is severely limited by virtue of its incorporation into reconstituted tobacco. Harshness associated with reconstituted tobaccos generally limits their use levels in cigarettes to 40 percent or less of the total weight of the cut filler. Thus, the examples in U.S. Pat. No. 4,256,123 describe cigarettes containing a maximum of 6 percent by weight of the pyrolyzed tobacco by-product component.
Related to the disclosures of various degraded carbohydrates as smoking materials is the use of binders and adhesives in converting the degraded carbohydrates into a stable, useful form. U.S. Pat. No. 3,844,294 discloses, for example, a smoking material based on thermally degraded carbohydrates which includes methylcellulose, sodium carboxymethycellulose, pectins and gums as binders or film-forming agents. Similar binders or adhesives are disclosed in U.S. Pat. No. 4,019,521 as well as a number of additional patents although they are generally used in combination with a variety of inorganic fillers, combustion control agents, ash cohesion agents, flavorants, etc. necessary for the preparation of an acceptable smoking material. Although the binders or film-forming agents are necessary for producing a coherent strand or sheet, such agents are also widly regarded as the source of objectionable odors and acridity commonly associated with smoking products containing them.